1. Field of the Invention
The invention relates to planispheres and refers more specifically to planisphere structure for accomplishing both astronomical and navigational calculations and displays. Specifically, the planisphere of the invention includes structure for and may be operated to provide either an overhead or a ground position display of heavenly bodies in both the northern and southern hemispheres at different longitudes and latitudes in a Copernican manner. Hour angle circle diagrams and navigator's time diagrams may be programmed on the planisphere of the invention which also provides structure for directly indicating altitude and azimuth of celestial bodies and navigation east and navigation west scales to enable a correct conceptual approach to navigation problems. Information concerning stars useful in navigation is also obtainable from the structure of the planisphere of the invention.
In operation, the planisphere may be programmed to provide an overhead or ground position display of the stars in either of the northern or southern hemispheres viewable from different predetermined latitudes on a predetermined day at a selected time in a Copernican manner. Further, hour angle circle diagrams and navigator's time diagrams may be solved on the planisphere of the invention to provide rapid, accurate information in conjunction with readily available printed reference material without the possibility of mathematical computation errors. Altitude and azimuth information with respect to celestial bodies is also available from the planisphere of the invention.
Also, the relative direction of navigational stars and their magnitude, declination and number are provided on one modification of the planisphere.
2. Description of the Prior Art
In the past, structure for astronomical and navigational displays and calculations have generally been restricted to use in either astronomy or navigation. Further, the prior structures have usually been limited to use in a single hemisphere and to a predetermined latitude.
No prior devices for solving hour angle circle diagrams or providing time diagram information without mathematical computation with the ease and facility of the planisphere of the invention or which provide a conceptually correct approach to navigation problems by the use of both navigation east and navigation west scales are known. In addition, while those engaged in prior navigational computations have sometimes incidentally used the Greenwhich meridian as a starting point, in accordance with the present invention and in the present system, the use of the Greenwich meridian as a starting point is emphasized.
Wherein navigational star information has been provided before, it has usually been in the form of charts and lists rather than on a planisphere scale in combination with other navigational and astronomical information.
In particular, the star finder and identifier number H.O. 2102-D previously published by and obtainable from the United States Naval Oceanographic Office is limited in practical use to finding and identifying stars. It cannot function as a substitute for a time diagram since the mean time scales necessary for that purpose are not available. Orienting the sky map for either hemisphere properly by directing the south meridian or the longitude position due south from the northern hemisphere standpoint and the north meridian due north in the southern hemisphere is the prime and only limited, practical purpose of H.O. 2102-D in the system of celestial navigation. Sight reduction according to present notions of time approximations of the nearest half-hour or so does not require accuracy with respect to azimuth and altude even to the extent of the grid application by rough interpolation provided by H.O. 2102-D. In case accuracy is a requirement for sight reduction, Tables of Computed Altitude and Azimuth, published by the United States Hydrograhic Office Publication H.O. 214, is a quickly available and more satisfactory source to serve that purpose.
Also, it will be noted that H.O. 2102-D is disintegrated with respect to the many parts of dissembled structure necessary to even its limited ultimate use, in contrast to the completely integrated, totally interrelated structure of the planisphere of the invention.